Page 101 - Dedola2011

l. Introduction
The species belonging to the genus Patella (Gastropoda: Patellidae) are known to have an
important intluence on the structure and function of the rocky shore communities, and
therefore are considered as crucial "keystone" species (Raffaelli & Hawkins 1996).
However, many of Patella species have long been recognised as taxonomically challenging
(Fisher-Piette 1938). Furthermore, the application ofmolecular methods has recently
contributed to reveal the occurrence of complexes of cryptic species even in taxa assumed
easy to identify in the field, such as Patella rustica Linnaeus, 1758 (Sa-Pinto et al. 2010).
Similarly, in Patella ulyssiponensis Gmelin, 1791 , one of the most widely distributed
limpet, the finding ofhigh leve] of genetic differentiation evidenced by the allozymes
between the populations from the Mediterranean and the north-eastern continental
shoreline of the Atlantic, and the populations from the Macaronesian islands, led Weber &
Hawkins (2005) to hypothesise the presence of two distinct species: P. ulyssiponensis from
the European continent, and Patella aspera Roding, 1798 restricted to the Macaronesia.
However, no consensus emerged on the taxonomic status of these populations, e.g. Sa-
Pinto et al. (2005, 2008) referred to the populations as continental and Macaronesian
"forms" of P. ulyssiponensis, respectively.
Among the European limpets, P. ulyssiponensis sensu lato is one of the most difficult to
identify, as it shows a broadly overlapping morphological variability with the other Patella
species living in the lower part of intertidal zone. This fact made the identification of
specimens with "intermediate" morphology impossible even for skilled observers (Fisher-
Piette 1938; Evans 1953; Sella et al. 1993). For instance, in the Mediterranean the
distinction between P. ulyssiponensis s. l. and the endemie Patella caerulea Linnaeus, 1758
is particularly troublesome. In severallocalities, neither the shell and foot colour pattern
nor the shell shape may allow to unequivocally discriminate between the two species

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Gìan Luca Dedola: ANALISI DELLA VARIABILITÀ GENETICA DI PATELLA FéRRUGINEA, PATEL-LA ULl'SSIPONENSIS (MOLLUSCA: GASTROPODA) E PINNA
NOBILIS (MOLLUSCA: BIVALVIA): lLCONTRJBUTO DEl DATI MOLECOLARI ALLA CONSERVAZIONE DI SPECIE MINACCIATE - Tesi di douorato in Scienze
della natura e delle sue risorse • indiri7.zo BK>logi.a Ambientale, Università degli Studi di Sassarl